This invention relates to a method for manufacturing tapered rods. More particularly, it relates to the method for manufacturing tapered rods and bars from a predetermined metallic material extremely efficiently, i.e., minimizing the material loss and maximizing the productivity, and also to an apparatus applicable for the method.
In recent times coil springs used for cars and railroad wagons have been gradually changed, for improving the comfortableness of riding to the passengers, from the conventional constant diametered ones to tapered coil springs made of tapered rods featured in the so-called nonlinear characteristics. The tapered rods employed for the rapidly prevailing tapered coil springs are provided with a larger diametered portion (a) in the central portion and a continuously diameter diminishing tapered portions (b) on either side of the former, as shown in FIG. 1. In one example, the ratio between the larger diametered portion (a) and the progressively diameter diminishing portion (b) is b:a:b=1:1:1, and the whole length L, i.e., (a)+2(b) designates the length of a material for one coil. In this way a rod having the larger diametered portion (a) in the central portion and the diameter diminishing portions (b) on either side is actually employed as a material in production plants of the tapered coil springs. In a coil spring made of a tapered rod of this type the varying trend of its height which is observed according to the variation of load is non-linear (A) as can be seen in FIG. 2, while in a conventional coil spring made of a constant diametered rod the trend of the height thereof as the load varies is regularly linear (B). This difference (A) and (B), i.e., the height in proportion to the load variation constitutes the difference in the comfortableness. In other words, the tapered coil springs showing the non-linear trend line of the height greatly contributes to the betterment of the riding comfort of various wagons.
The tapered rods as material of the tapered coil springs have been conventionally manufactured chiefly by machining wires or rods of a desired metallic material. Machining of the metallic material naturally yields a great deal of material loss, and needs in addition much of the time, remarkably degrading the productivity.
In some quarters hot forgoing method which is called rotary swaging method employing a swaging machine is adopted to manufacture this type of tapered rods. This method is meritorious indeed in diminishing the material loss, leaving however inevitable long machining hours still unchanged.
All of the conventional manufacturing methods of the tapered rods were extremely low in productivity. And no appreciably improved apparatuses or systems were developed for the solution of the above-mentioned problems.